US 2783441 A
Description (OCR text may contain errors)
1957 G. CAMILLI ETAL TRANSFORMER 2 Sheets-Sheet 1 Filed July 25, 1952 Inventors: Guglielmo Camilli, George |-I.Halsey,
y Their Attorne 2 Sheets-Sheet 2 TRANSFORMER G. CAMILLI ETAL Feb. 26, 1957 Filed July 25, 1952 Fig.5.
Inventors: Guglielmo Camilli, George H. Halse g,
Z/Qywtfl Their Attorney.
United States Patent TRANSFORMER poration of New York This invention relates to transformers and more par ticularly t0 coils for'transformers-of the dry type.
In the conventional dry-type transformer construction,-a lami'natetl core is provided with two or more vertically arranged leg portions. In a single phase trans former, the windings are conventionally arranged on one or two of the legs while in a three-phase transformer, windings are arranged on each of-the legs. (Considering only one core log, it has been the practice to mount a sleeve -or cylinder of insulating material on the leg with the low voltage winding being wound thereon. This assembly is in turn surrounded by another cylinder of insulating material on 'whichiis wound the high voltage winding. The high voltage winding has conventionally beeniformcd of a plurality of axially spaced apart 'horizontally arranged disloshaped annular coils spaced from the outer Pinsu'lating cylinder by .axiallyextending spacing members. This arrangement permits cooling air to be circulated through the space :between the inner periphery of the disk coil's and the outer cylinder and, of course, over the outer-periphery'of the coils.
The efliciency of convective heat transfer from such horizontal disk-coils to the air surrounding the coils depends upon the thickness of the stagnant boundary layer of airclinging to the surface of the coils. This boundary layer of air acts as't'nermal insulationand determines the local surface temperature rises over the local ambient temperature. These slow moving boundary layers of air tend to b'ecomequite thick reducingthe-convective heat transfer coefficient, particularly when the ventilating path through thec'oils is long and-arduous. It has been found that from a thermal standpoint, the conventional horizontal disk coils were very inefficient andtit is therefore desirable to provide a disk type coil arrangement which will produce a reduction in the temperature rises over. the surrounding ambient.
It is therefore an-object fof this2i11venti0n2to1provide an improved transformer construction having disk-type coils wherein the thermal eiiiciency is increased.
Further objects and advantages of this invention will become apparent by reference to the following description and the accompanyingdrawing, and the features of novelty which characterize --this invention will be pointed out with particularit-yin theclaims annexed to and forming a part of-thisspecification.
This i'nvention i-n its broadest aspects provides a diskshaped annular transformer-coil having a plurality of sections, these sections being radially spaced apart thereby dfiriin'gannul-ar ducts-for ventilating the coil. The splitting ofdisk coils into severalr-adizilly spaced apart sections reduces *the effective tot-a1 length "of air flow path up through the coils -therebyincreasing the amount of air flow for a given heat 'dissipation giving lower air temperatures surrounding the coil. Furthermore, the stagnant'air film thickness 'cli'nging"'to'the coil surfaces is greatly reduced with the net result that the local heat transfer coefiicient is increased and the temperature rise of the coil over local air is substantially reduced.
'In the drawing, Fig. l is a fragmentary broken away view showing a dry type transformer of conventional construction;
Fig. 2 is a fragmentary cross-sectional view showing the arrangement of the high voltage coils of the transformer of Fig. l and the path of the air flow through the coils;
Fig. 3 is a fragmentary side elevational view, partly in section, illustrating a transformer provided with the improved split high voltage coils of this invention;
Fig. 4 is a vertical view, partly in section, taken along the line 44 of Fig. 3;
Fig. 5 is a fragmentary cross-sectional view showing the improved split coil construction of Figs. 3 and 4 and the air flow thereth-rough;
Fig. 6 is a fragmentary cross-sectional view taken along the line 6-6 of Fig. 4.
Fig. 7 is a fragmentary cross-sectional view illustrating a modified form ofthis invention;
Fig. 8 is a'fragrnentary cross-sectional view taken along the line SS of Fig. 7; and
Fig. 9 is a circuit diagram schematically illustrating one connection for the improved split coils of thisinvention.
Referringnow to Fig. 1, there is shown a'portionof a vertically arranged leg 1 of a transformer core formed of 'a plurality of relatively thin laminations of magnetic material 2. The leg} is surrounded'by a cylinder 3 formed of insulating material which in turn is embraced by a plurality of axially spaced apart disk-type low voltage coils 4. The low voltage coils 4, which are .each formed from a radially wound'continuous conductor 5, are wound on axial spacersfi formed of insulating material and outer cylinder 7, also formed of insulating material, is supported thereon by means of axial spacerstl. High voltage winding 9is wound overthe outer cylinder 7 and comprises a plurality of horizontal spaced apart disk type coils 10 Wound on axial spacing members 8' formed of suitable insulating-material. Here again, each of the coils 10 is formed from a continuous radially wound conductor 1:1 with each coil being electrically connected ito the adjacent coils to form the complete high voltage winding 9. Spacing members 12 maintain the proper axial spacings'between the disk coils 10.
Referring nowto'Fig. 2, there is shown a fragmentary cross-sectional vie-w'of the high voltage winding9 of Fig. l. Itwill be seen that the ventilating air flows between the'coils 10 and the cylinder7, as shown by the arrows 13 and over'the outer-periphe-ry-of the coils asshown by the arrows '14. It will also be seen t-hat the circulating air '13 and "14 only partially-enters the spaces between the coils 10 thereby resulting in an area ofstagnant air 15 between the "coils and aslow moving boundary layer16 adjacent theedges of'the-coils. It has been found that the thickness o f-the boundary layer varies approximately as the M1 power ofthe distance from-the edge of the coil tothe center, as shown by the dimension 17.
Referring now to Figs. '3, '4 and '5, in'which like elements are'indicated*by'-'lil e reference numerals, 'itis seen that the laminated core 1 is again surrounded by inner insulating cylinder S'vvhichin'turn is surrounded by low' voltage winding coils 4. Coils 4 are wound on axial spacing members 6 and are spaced apart by spacer members 18. Outer cylinder 7 is again mounted-endow voltage coils 4 bymeans'of axial-spacing members'*8. Inorder to improve the thermal e'fliciency,'however, thehigh voltage coils 19 areeafch divided'into an inner section 20 andan outersection 2'1, theinnersection 2'0-being-radiallyspaced from thecylinder 7 thus defining an annular ventilating duct 22 and'the outer'section 21 beingradizilly=spaced from the inner section 20 thus defining another annular ventilating duct 23. Here, each inner coil section 20 is formed of a continuous radially coiled conductor 24 and each outer coil section 21 is similarly formed of a contlnuous radially coiled conductor 25. A crossover 26 connects the outer end of conductor 24 of coil section 20 to the inner end of conductor 25 of coil section 21, while another crossover 27 connects the outer end of conductor 25 of coil section 21 to the inner end of the inner section of the adjacent coil. It is thus seen that the outer and inner sections of each coil are serially connected while each complete coil is in turn serially connected to form the high voltage winding of the transformer.
In order to provide for the necessary radial and axial spacing of the coil sections 20 and 21, a plurality of radially extending spacing members 28 are arranged between the coils 19 with radial spacers 29 and 30 being suitably secured thereto to provide the requisite radial spacing. The spacing members 28, 29 and 30 are all formed of insulating material and are more fully described in copending application, Serial No. 300,904, filed July 25, 1952, now Patent No. 2,756,397, of Curtis M. Cederstrom, Lloyd S. Blair and John C. Russ assigned to the assignee of the present application.
Referring now to Fig. 5, it is seen that the effective total length of air flow path up through the coils is decreased with air flowing through the inner duct 22 as shown by the arrow 31, through the outer duct 23 as shown by the arrows 32 and '33, and over the outer periphery of the coils as shown by the arrow 34. It is readily seen that the width of the stagnant air area between each coil section is much smaller than that found in the prior art arrangement of Fig. 2 and that by splitting the disk coils into two parts, the distance 17 from the edge of each coil to the center line thereof is cut in half and thus the heat transfer coefiicient is increased by 2% or 19%. It has been found that in large dry type power transformers, the width of the gap 23 should be between /2 inch and /1, inch. It is now readily seen that the construction of Figs. 3, 4 and 5 increases the amount of air flow for a given heat dissipation thus giving a lower air temperature surrounding the coil sections and also reducing the stagnant air film thickness clinging to the coil section surfaces, thereby increasing the heat transfer coefiicient and reducing the coil temperature rise over the local ambient air temperature.
Referring now to Figs. 7 and 8 in which like parts are again illustrated by like reference numbers, there is shown a modified form of this improved transformer coil construction. It will be readily seen that the adjacent disk coils 19 of the construction of Figs. 3, 4 and 5 must be connected together by means of conductor 27 which must cross the total radial build of each disk coil. This necessitates hand taping which may be both slow and delicate. To obviate the necessity for this operation, the arrangement of Figs. 7 and 8 may be used. Here, a plurality of inner disk coils 35 are first wound on the outer cylinder 7, being spaced therefrom by means of axial spacing members 36 formed of suitable insulating material. Each disk coil 35 is formed of a continuous radially wound conductor 37 and each disk coil 35 is connected to its adjacent inner disk coil. The inner disk coils 35 are axially spaced apart by means of suitable spacers 38 also formed of insulating material. After all of the inner disk coils 35 are wound, outer longitudinal spacing members 39 are positioned in slots 40 in the spacing members 38 and outer disk coils 41 are wound thereon again being separated by spacers 38. The disk coils 41 are similarly formed of a continuously radially wound conductor 42 with all of the outer disk coils 41 being electrically connected to form a continuous winding. The
inner disk coils 35 thus form an inner winding section and the outer disk coils 41 form a separate outer winding section, these two sections then being electrically connected in parallel to form the complete winding.
In order to insure that the current is evenly divided be tween coils of the inner and outer sections of the windings of Figs. 7 and 8, the electrical connection of Fig. 9 may be employed wherein inner coils 43 and 44 are cross connected to outer coils 45 and 46, the resultant serially connected coils 43 and 46, and 44 and 45 being connected in parallel across lines 47 and 48. This arrangement will insure that the current divides equally between the two winding sections.
While the improved disk coil of this invention has been shown as comprising two sections, it will be readily apparent that it may comprise more radially spaced apart sections than the two shown. It will also be readily understood that while air has been referred to as a ventilating medium, this construction may actually be used in any gaseous insulated transformer. It will now be readily seen that this invention provides an improved transformer coil construction characterized by its improved thermal efiiciency and lower temperature rise.
While we have shown and described specific embodiments of this invention, further modifications and im-v provements will occur to those skilled in the art. We desire it to be understood, therefore, that this invention is not limited to the form shown and we intend in the appended claim to cover all modifications which do not depart from the spirit and scope of this invention.
What we claim as new and desire to secure by Letters Patent of the United States is:
In a transformer, a cylindrical mounting member, a plurality of disc-shaped annular coils coaxially arranged on said mounting member, axially extending spacers between said mounting member and said coils to provide a first annular ventilating duct, radially extending spacers between said coils to provide ventilating ducts between said coils, each of said coils being comprised of an inner close spirally wound section of a plurality of turns and an outer close spirally wound section of a plurality of turns, and spacing means between each of said inner and outer sections to provide a second annular ventilating duct, the inner sections of substantially one-half of adjacent said coils being serially connected, the outer sections of said one-half of said coils being serially connected, the inner sections of the other half of adjacent said coils being serially connected, the outer sections of said other half of said coils being serially connected, said serially connected inner sections of said one-half of said coils being connected in series with said serially connected outer coils of said other half, said serially connected inner sections of said other half being connected in series with said serially connected outer coils of said one-half, said serially connected inner and outer sections being parallel connected.
References Cited in the file of this patent UNITED STATES PATENTS 717,006 Johannsen Dec. 30, 1902 772,288 Neall Oct. 11, 1904 834,160 Nichols Oct. 23, 1906 873,166 Nichols Dec. 10, 1907 974,167 Mayer Nov. 1, 1910 1,747,953 Roothaan Feb. 18, 1930 2,201,005 Ford May 14, 1940 2,279,028 Weed Apr. 7, 1942 2,295,371 Vogel Sept. 8, 1942 2,337,916 Meyerhans et a1 Dec. 28, 1943 2,388,565 Paluev Nov. 6, 1945 2,422,037 Paluev June 10, 1947 7 2,527,236 Whitman Oct. 24, 1950 FOREIGN PATENTS 734,631 Germany Apr. 20, 1943 raw-1